1. Field of the Invention
The present invention relates to a method for rehabilitating a manhole, in particular to a method for rehabilitating a corroded or damaged existing manhole by reinforcing an inner circumference of a sidewall of the manhole.
2. Description of the Prior Art
The following two typical methods are known to rehabilitate a manhole.
A first method for rehabilitating a manhole is disclosed in Japanese Patent Laid Open Publication No. 1996-150659. This method uses a lining material consisting of a flexible resin absorbing material which has a cylindrical bag shape corresponding to a shape of the inner circumferential surface of the manhole and which is impregnated with a liquid thermosetting resin. The lining material is folded for insertion into the manhole, and pressed from the inside thereof against the inner circumferential surface of the manhole by the pressure of water. The lining material is then heated using a hot water shower, so that the liquid thermosetting resin impregnated therein is cured to provide a rehabilitating pipe for the manhole.
A second method for rehabilitating a manhole is disclosed in Japanese Patent Laid Open Publication No. 2005-307577, in which a pipe-shaped body is assembled in the manhole to provide a rehabilitating pipe whose outer diameter is slightly smaller than an inner diameter of the manhole and whose inner circumferential surface constitutes a cylindrical. surface. For this purpose, the method uses a plurality of segments each of which is integrally molded of plastics and has a shape obtained when the rehabilitating pipe is divided respectively into a plurality of parts in the circumferential direction and the vertical direction (pipe longitudinal direction). A plurality of segments thus formed is successively inserted into the manhole, then coupled in the circumferential direction and stacked in the vertical direction, thereby assembling the rehabilitating pipe. Thereafter, a gap between the manhole and the rehabilitating pipe is filled with a filler. The filler is then hardened to integrate the rehabilitating pipe and the manhole, thus providing a compound pipe.
However, in the first method, the lining material inserted into the manhole is subjected to flooding, showering by hot water, and draining of the hot water. This requires large-scaled and expensive instruments or equipments such as boilers, tanks, pumps, various kinds of hoses, and the like. The first method is thus disadvantageous in cost. Further, the first method requires that a boiler car equipped with the boiler parks on a road in the construction site. Consequently, the boiler car, or the like inevitably occupies a large area on the road, thereby giving a large influence on the traffic.
The second method is also disadvantageous in cost because the segments are required for constructing the rehabilitating pipe. Namely, in order to reduce the cost of the segments each of which is integrally formed of plastic, it is necessary to mass-produce a single kind of the segments having the same shape and size. On the other hand, a large number of the segments are not needed for rehabilitating a manhole. In addition, the rehabilitating pipe cannot be constructed from the single kind of the segments because it depends upon the shape of the inner circumferential surface of the manhole. For example, the upper portion of the rehabilitating pipe has a hollow circular truncated cone form while the other lower portion has a hollow column form. In this case, the segments the same in shape and size can be used to assemble the lower portion of the rehabilitating pipe. On the other hand, the segments having different sizes from each other are needed to assemble the upper portion of the rehabilitating pipe that has the hollow circular truncated cone form, thus increasing the cost for producing the segments used for the upper portion of the hollow circular truncated cone form of the rehabilitating pipe.